selftests: enhance membarrier syscall test

selftests: enhance membarrier syscall test

Update the membarrier syscall self-test to match the membarrier interface.
 Extend coverage of the interface.  Consider ENOSYS as a "SKIP" test,
since it is a valid configuration, but does not allow testing the system
call.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Pranith Kumar <bobby.prani@gmail.com>
Cc: Shuah Khan <shuahkh@osg.samsung.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>